1. Field of the Invention
The present invention relates to a projector for projecting images on a projection object such as a screen, and particularly relates to a projector comprising a zoom lens for which it is possible to change the size (projection scope) of the projection image that is projected, and an imaging unit for imaging the projection images, and a control method for this projector.
2. Description of the Related Art
With projectors in recent years, projectors are known for which a zoom lens is provided as the projection lens, and by driving that zoom lens and changing the zoom volume of that zoom lens, the projection scope of the images formed on the screen can be changed freely.
When installing this kind of projector in front of a screen, it is necessary to perform various adjustments such as zoom adjustment, keystone calibration, focus adjustment, and the like on the projector in advance so that a suitable image is displayed on the screen by the projection light projected onto the screen from the projector.
However, in the case of a portable projector, since there is the possibility that the relative position of the projector and the screen will change when installing a projector, the user had to perform the various adjustments like those noted above at that time, which was very complicated.
In light of this, as noted in Japanese Patent Laid-Open Gazettes No. 2000-241874, for example, conventionally, together with providing a monitor camera in a projector, when installing that projector in front of the screen, first, an adjustment pattern image was projection displayed on the screen by the projector, the screen for displaying that pattern image was imaged by a monitor camera, that imaged image was analyzed, and based on those analysis results, each of the aforementioned types of adjustment was performed automatically.
Generally, the aforementioned monitor camera comprises a CCD (Charge Coupled Device) or the like for converting the light made incident from the lens to electrical signals, and to make the overall imaged image brightness to a preset value (exposure target value), there is an automatic exposure adjustment function for changing the shutter speed, gain (sensitivity), aperture, and the like.
FIG. 9 is an explanatory drawing for explaining the effects of the automatic exposure adjustment function of a conventional monitor camera. In FIG. 9, the upper level indicates a screen for displaying an adjustment pattern image, the middle level indicates the imaged image obtained by imaging that screen using the monitor camera, and the lower level indicates a value representing the brightness of each pixel along the center horizontal line (dotted line) in that imaged image. Also, FIG. 9 (A) shows the status of the projector when set to normal luminance, and FIG. 9 (B) shows the status of the projector when set to low luminance. Note that the value representing the brightness of each pixel for the imaged image is called a gradation value hereafter. This gradation value is a value obtained from image signals of the imaged image output from the monitor camera (CCD module). Also, as illustrated, the projection scopes in FIGS. 9 (A) and (B) are the same.
In FIG. 9, the adjustment pattern image is an all white image, and as shown in the top level, in the screen, the white part scope displayed as the adjustment pattern image is the aforementioned projection scope. The imaged image obtained by imaging using the monitor camera is as shown in the middle level. Also, in the bottom level, the horizontal axis corresponds to the position of each pixel on the center horizontal line of the imaged image, and the vertical axis indicates the gradation value of each pixel.
At the projector, when the luminance of the light source lamp is set to low luminance, compared to when set to normal luminance, the luminance of the projection light projected from the projector is low. Because of this, as shown in FIG. 9 (B), the brightness of the adjustment pattern image displayed on the screen is also dark compared to when set to normal luminance as shown in FIG. 9 (A). However, when that adjustment pattern image is imaged by the monitor camera by operating the automatic exposure adjustment function, even if the object is dark, the shutter speed, gain, and aperture and the like are adjusted to achieve a suitable brightness for the overall imaged image, so with that imaged image, as shown in FIG. 9 (B), the brightness of the adjustment pattern image is not different from when set to normal luminance as shown in FIG. 9 (A). Therefore, for the imaged image, the black part, specifically, the part other than the projection scope, is dark at a negligible level, so in contrast to regarding the gradation value of each pixel for the black part as 0, the gradation value of each pixel of the white part, specifically the adjustment pattern image part, is left approximately at the desired gradation value Lt, and does not change.
In this way, by operating the automatic exposure adjustment function with the monitor camera, at the projector, when the light source lamp is set to low luminance, even when the brightness of the adjustment pattern image displayed on the screen is dark, for the imaged image, the gradation value of each pixel of the white part, specifically the adjustment pattern image part, may be maintained approximately at the desired gradation value Lt, the same as when set to the normal luminance. This is not limited to when set to low luminance, but is also the same when the light source lamp degrades over time and its luminance decreases.
However, for the projector comprising the zoom lens and the monitor camera described above, when the zoom volume of the zoom lens is changed and the projection scope on the screen is changed, due to the automatic exposure adjustment function of the monitor camera, the following kinds of problems occurred.
FIG. 10 is an explanatory drawing for describing problems due to the automatic exposure adjustment function of the monitor camera when changing the zoom volume with the conventional art. In FIG. 10, the same as FIG. 9, the upper level shows the screen on which the adjustment pattern image is displayed, the middle level shows the imaged image of that screen, and the lower level shows the gradation value of pixels in that imaged image. Also, FIG. 10 (A) shows the status when the zoom volume of the zoom lens is changed to an intermediate value, FIG. 10 (B) shows the status when the zoom volume of the zoom lens is set to the wide angle side (larger) compared to the intermediate value, and FIG. 10 (C) shows the status when the zoom volume of the zoom lens is set to the telephoto angle side (smaller) compared to the intermediate value.
When the zoom volume of the zoom lens is set to the wide angle side compared to the intermediate value, as shown in the upper level of FIG. 10 (B), the area of the projection scope on the screen is wider than when set to the intermediate value of FIG. 10 (A), and the displayed pattern image is also expanded. Therefore, when the adjustment pattern image is imaged by the monitor camera as shown in the middle level of FIG. 10 (B), in the imaged image, the white part, specifically, the area of the adjustment pattern image part, is wider than when set to the intermediate value of FIG. 10 (A), and the area of the black part, specifically, the part outside the projection scope, becomes narrower.
At this time, when imaging is performed by the monitor camera by operating the automatic exposure adjustment function, the brightness of the overall imaged image is calculated as the exposure calculated value, and so that the exposure calculated value is equal to the preset exposure target value, the shutter speed, gain, aperture, and the like are controlled. Here, the brightness of the overall imaged image is the sum of the volume of the light detected for each pixel with the CCD that was converted to electrical signals and amplified, and that value is proportional to the average value of the gradation value of each pixel for that imaged image. Thus, normally, the exposure calculation value uses the average value of the gradation values of all pixels for the imaged image.
Meanwhile, because the exposure target value is a preset specified value, as shown in FIG. 10 (A), when setting the zoom volume to an intermediate value, if the exposure calculation value matches the exposure target value, as described above, when the zoom volume is set to the wide angle side compared to the intermediate value, and the area of the white part of the imaged image becomes wider, then the average value of the gradation value of all the pixels, specifically, the exposure calculation value, increases compared to the exposure target value by the amount that the are became wider. As a result, when the automatic exposure adjustment function is operated and the shutter speed, gain, aperture and the like are changed so that the exposure calculation value is equal to the exposure target value, the average value of the gradation values of all the pixels for the imaged image decreases. As described above, for the imaged image, the black part is dark to a negligible level, and the gradation value of each pixel for the black part is regarded as 0, so the decrease in the average value of the gradation values for all the pixels means that the gradation values of each pixel for the white part is decreased more than the desired gradation value Lt, as shown in the lower level of FIG. 10 (B).
Conversely, when the zoom volume of the zoom lens is set to the telephoto side compared to the intermediate value, as shown in FIG. 10 (B), the area of the projection scope on the screen becomes narrower compared to when set to the intermediate value of FIG. 10 (A), and the displayed pattern image is also reduced. Therefore, when that pattern image is imaged by the monitor camera, as shown in the middle level of FIG. 10 (C), the area of the white part, specifically, the adjustment pattern image part for that image image is narrower than the intermediate value of (A), and the area of the black part, specifically, the part outside the projection scope, becomes wider.
When the area of the white part of the imaged image becomes narrower, the average value of the gradation values of all the pixels, specifically the exposure calculation value, becomes lower than the exposure target value by the amount that the area narrowed. As a result, when the automatic exposure adjustment function is operated and the shutter speed, gain, aperture, and the like are changed to make the exposure calculation value equal to the exposure target value, the average value of the gradation values of all the pixels for the imaged image increases, and as a result, as shown by the lower level of FIG. 10 (C), the gradation values of each pixel of the white part becomes larger than the desired gradation value Lt.
As described above, conventionally, when the zoom volume of the zoom lens was set to the wide angle side compared to the intermediate value, and the projection scope on the screen became wider, due to the automatic exposure adjustment function of the monitor camera, the gradation values of each pixel of the white part for the imaged image decreased more than the desired gradation value Lt, and conversely, when set to the telephoto side compared to the intermediate value and the projection scope became narrower, the gradation values of each pixel of the white part became greater than the desired gradation value Lt, and in either case, it was not possible to maintain the average value of the gradation values of the white part at the desired gradation value Lt.
Therefore, by changing the zoom volume of the zoom lens, when the average value of the gradation values of the white part for the imaged image is distanced from the desired gradation value Lt, after that, as described above, the imaged image is analyzed, and based on the analysis results, when various adjustments are made automatically, depending on the adjustment contents, there was the problem of not being able to perform adjustments properly.
This kind of problem is not limited to when the adjustment pattern image is all white, but may also similarly occur in cases when it is a specific color (e.g. green, etc.) other than white, or when it is part rather than all of the image.